Pap Testing as Primary Screening

ASC-US Triage Using HPV Testing

"Atypical squamous cells of undetermined significance (ASC-US)" is considered an inconclusive pap test result that requires follow-up testing to determine appropriate patient management. An ASC-US pap test result may be triaged using repeat cytology, colposcopy, or HPV testing. HPV testing is the preferred triage strategy when using liquid-based cytology. "Reflex HPV testing" is easily performed as a follow-up test by utilizing residual cells from the liquid-based pap test vial to test for the presence or absence of high-risk HPV. The ThinPrep Pap Test is the only liquid-based pap test with FDA approval for out-of-vial HPV testing.

ALTS Trial — NCI-sponsored study

The ASCUS/LSIL Triage Study (ALTS) was conducted by the National Cancer Institute (NCI) to determine effective strategies to manage ASC-US pap test results. The study included 3488 women with an ASC-US pap test result, and compared 3 strategies for follow-up: 1) immediate colposcopy; 2) repeat cytology with referral to colposcopy if HSIL or greater; and 3) HPV testing. The study reported that the triage sensitivity of HPV testing was 95.9% for detecting CIN 2 +. A little over half of the women in the study were positive for HPV, which required referral to colposcopy.1

ACOG guidelines on ASC-US triage

American College of Obstetrician-Gynecologists (ACOG) guidelines state that when liquid-based cytology is used at the time of the initial visit, HPV testing for ASC-US "eliminates the need for a repeat office visit and is a more sensitive triage tool than repeat cytology while referring fewer women to colposcopy."2

ASCCP — 2006 Consensus Guidelines

The Consensus Guidelines of the American Society for Colposcopy and Cervical Pathology (ASCCP) state that HPV testing, repeat cytology, or colposcopy are all acceptable methods for managing women older than 20 years with ASC-US pap test results. When liquid-based pap tests are used, "reflex HPV Testing" is the preferred approach.3


1. Schiffman M, Soloman D. Findings to date from the ASCUS-LSIL Triage Study (ALTS). Arch Pathol Lab Med. 2003;127(8):946-9.

2. ACOG Practice Bulletin, no 61, April 2005.

3. American Society of Cytopathology. American Society of Cytopathology statement on new technologies in cervical cytology screening. June 2000. Acta Cytol. 2000;44(4):693.

See a list of key studies involving the ThinPrep
Pap Test and the ThinPrep Imaging System.

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